<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<style>
    * {
        margin: 0;
        padding: 0;
    }

    ul,
    ol {
        list-style: none;
    }

    .box {
        width: 300px;
        height: 250px;
        border: 2px solid hotpink;
        margin: 200px auto 0;
    }

    ul {
        overflow: hidden;
    }

    ul li {
        background: orange;
        width: 98px;
        height: 50px;
        border-left: 1px solid black;
        border-right: 1px solid black;
        float: left;
        font: 20px/50px "";
        text-align: center;
    }

    ul li.active {
        background-color: orangered;
    }

    ol li {
        background: skyblue;
        width: 300px;
        height: 200px;
        font: 50px/200px "";
        text-align: center;
        display: none;
    }

    ol li.active {
        display: block;
    }
</style>

<body>
    <div class="box">
        <ul>
            <li class="active">1</li>
            <li>2</li>
            <li>3</li>
        </ul>
        <ol>
            <li class="active">1</li>
            <li>2</li>
            <li>3</li>
        </ol>
    </div>
</body>
<script src="./jquery/jquery.min.js"></script>
<script>
    $("ul li").mouseenter(function () {
        //1.
        // $(this).addClass("active").siblings().removeClass("active").parent().next().find('li').eq($(this).index()).addClass('active').siblings().removeClass('active')
        //2.
        $(this).addClass("active").siblings().removeClass("active").parent().next().children().removeClass("active").eq($(this).index()).addClass("active")
    })
</script>

</html>